Method for the detection of whistling in an audio system

Abstract

A method for detecting whistling in an audio system includes determining an average frequency of an input signal of the audio system, sampling the input signal in consecutive blocks of at least one sample, wherein the average frequency is determined blockwise, and determining whether feedback related whistling is present in the input signal of the audio system by evaluating a stability of the average frequency, wherein the evaluation of the stability of the average frequency comprises: determining a difference of two values of the determined average frequency for two blocks, and comparing the determined difference to a first threshold value.

Description

PRIORITY DATA[0001]This application claims priority to, and the benefit of, Danish Patent Application No. PA 2009 70303, filed on Dec. 29, 2009.FIELD[0002]The present application relates to a new method for the detection of whistling in an audio system in general and a hearing aid in particular. Furthermore, the present application relates to a hearing aid for execution of said method.BACKGROUND[0003]In a hearing aid it may occur that a fraction of the sound that that emanates from the receiver of the hearing aid may leak back to the microphone. This sound that leaks back to the hearing aid microphone will then be added to the microphone signal and amplified again. This process may thus be self-perpetuating and may even lead to whistling when the gain of the hearing aid is high. This whistling problem has been known for many years and in the standard literature on hearing aids it is commonly referred to as feedback, ringing, howling or oscillation.[0004]Usually the onset of whistlin...

AI Technical Summary

Benefits of technology

[0008]It is thus an object to provide a computationally effective and reliable method for the detection of whistling in hearing aids.

Problems solved by technology

In a hearing aid it may occur that a fraction of the sound that that emanates from the receiver of the hearing aid may leak back to the microphone.

This process may thus be self-perpetuating and may even lead to whistling when the gain of the hearing aid is high.

Hence, whistling thus poses a limit on the maximum gain that may be achieved in most hearing aids.

However, this solution to the problem of whistling is unsatisfactory, because the whistling is annoying for the user of the hearing aid, and the experience of whistling is usually painful and may even be directly harmful to the individual that experiences it.

There are however, several drawbacks of this method of whistle detection and whistle suppression.

First, the method disclosed in U.S. Pat. No. 6,650,124 does not disclose any efficient way of determining which frequency components of the input signal of the hearing aid needs to be analyzed by the variance criterion (in fact it is not clear how the signal is estimated, since U.S. Pat. No. 6,650,124 is silent with respect to this).

Secondly, the application of a variance criterion comprises the calculation of a 2'nd power (a squaring calculation), which is a complicated arithmetical operation that requires much processing power and in addition to this a much wider dynamic range (e.g. when a 16 bit number is squared it becomes a 32 bit number), especially if one consider the limited processing power that is available in present day hearing aids.

Thirdly, the proposed method of whistle suppression by the use of a notch filter is very inflexible and since a notch filter simply filters out a given frequency or a very narrow frequency region around a given frequency, the application of a notch filter for whistle suppression may lead to audible changes or distortions of the signal, which may be heard and perceived as annoying for a user.

Furthermore, the predetermined width of the notch filter will imply that it in some circumstances will be too wide, while it in other circumstances will be too narrow, and in case of a false detection of whistling the application of the notch filter will lead to a perceptual loss of signal power.

For example a moving average lower than 9 blocks will lead to that the method will react to transients in the input signal, while a larger moving average may lead to a too slow reaction.

Such a hearing aid with a whistle detector that is adapted to execute a method as described above is especially applicable to hearing small hearing aids that are openly fitted or have a large ventilation canal, because for those kind of hearing aids the feedback path may be so short that an adaptive feedback cancellation filter in some certain situations may not be able to suppress the whistling efficiently enough.

This may be annoying for the user, and may in certain situations even worsen the user's perception of speech.

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